Dendritic protein synthesis is essential for several forms of long-term synaptic plasticity that are thought to underlie learning and memory. However, the molecular mechanisms that regulate activity-induced dendritic translation remain unclear. One hypothesis is that activity may regulate mRNA binding proteins (RBP) that control the dendritic localization and translation of specific mRNAs. This proposal investigates the role of the RBP cytoplasmic polyadenylation element binding protein 1 (CPEB1) in dendritic mRNA targeting and local translation. The overall hypothesis is that CPEB1 associates with a multi-protein dendritic complex that regulates activity-induced transport and translation of known CPEB1 target mRNA CaMKIIa. The first aim of this proposal examines 1) dendritic localization of the multi-protein complex in CPEB1 null neurons compared to wild type and 2) the molecular mechanisms mediating activity regulation of the CPEB1 complex at synapses. The two proposed approaches for this aim are high-resolution quantitative immunofluorescence in cultured hippocampal neurons and biochemical analysis of synaptic fractions. The second aim addresses whether the CPEB1 complex regulates basal and activity-induced dendritic localization of CaMKIIa mRNA. CaMKIIa mRNA localization will be assayed in CPEB1 null neurons and following lentiviral-mediated knockdown of the CPEB1 complex proteins using in situ hybridization and live imaging of a tagged mRNA construct. The third aim evaluates whether the CPEB1 complex regulates dendritic CamKlla mRNA translation using live-cell imaging of a fluorescent mRNA reporter combined with lentiviral-mediated manipulation of the CPEB1 complex components. Consistent with the mission of NINDS to "pursue an understanding of the normal activities" of neurons, this proposal examines a potential mechanism by which activity might regulate the local synthesis of new proteins. This work contributes to the basic knowledge that founds the development of useful therapies for disorders of synaptic function. Lay summary: Deficits in learning and memory are symptoms of varied neurological conditions such as mental retardation, autism, traumatic brain injury and Alzheimer's disease. The proposed study investigates the regulation of experience-dependent modification of neuronal connections - the biological process that is thought to underlie learning and memory. Acquiring this basic knowledge is critical for understanding the pathology of these wide-spread disorders as well as the establishment of useful therapies.